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I would like to make a map displaying how several building uses have changed during the last decades. For example, this building was built in the year 1483 as a monastery, in 1880 it turned into a seminary and since then it has been a prison (1936-1939), has been abandoned (1939-1940), then transformed into a boarding school (1940-1998) and currently is a camping house (1998-present time).

I was thinking of adding two new date fields start_date and end_date in the layer with the geometry and other attributes and then combine everything with TimeManager plugin so I could dynamically see the evolution. Unfortunately that's not enough, as 1) the uses may change whereas the geometry will be the same one; and 2) that would only allow me to have a single use per row instead of having a complete uses' history. That made me think that I need to have more than one row for the same building if I want to have a "history" of uses. For that reason I was then thinking of creating a layer for the geometry and a different one for the building uses with the following fields:

  • id
  • geometry_id
  • description
  • start_date
  • end_date

By doing this I could easily "relate" a single geometry with one or more uses (each of them being a different row, each one having its own start and end dates). Unfortunately I do not know how can I relate both layers in an easy and fast way (preferably using GUI - I don't think that doing a regular join would be enough, as I have no easy way to know the geometry_id values beforehand) nor I am sure that is the best approach to do so (looks somewhat complicated to manage if I have many buildings' that I want to keep track of their changes, as it is the case).

What would you recommend me to do?

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You could put more than one geometry onto each other. Then you can have your full set of rows with your history. And in case of the same geometry but different usage you have two times the same geometry "above" each other. That should be like a relate.

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  • Thank you for your answer! Could you elaborate a little more? I am not sure of having understood the work flow. Correct me if I'm wrong, Are you suggesting to create a single layer for geometry with date end and date start attributes and then duplicating (or triplicating) the geometry and then change its dates' values? – ccamara Apr 23 '16 at 6:37
  • i think that is the temporary solution, extra duplicated layer with different time values since This Time Manager plugin does not allow us to insert a same layer twice where extra "start_time" field can be used – Uje Indo Apr 24 '16 at 14:56
  • thanks @UjeIndo , are you suggesting to duplicate layers per date? if so, I'm afraid that's overkill and I do not think is viable for my project, as I have a lot of geometry that would need to duplicate whenever some small parts of them may have a different value on the date field. I would end up with thousands of layers. – ccamara Apr 25 '16 at 9:34

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